[magick-users] Counting and differing pixels transparent and non-transparent

[Anthony Thyssen]

On Thu, 24 Sep 2009 15:06:44 -0700
Fred Weinhaus <fmw at alink.net> wrote:

| 1) extract the alpha channel (presumably as a binary image) white as 
| opaque and black as transparent
| 
| convert image -alpha extract alphachannel.png
| 
| 2) in a loop extract each column (see subsectioning 
| [1xheight+xoffset+0] or -crop ... +repage) and sequence down the 
| column (y increases downward in pixels) until you find the first 
| pixel that is white -- that will be the highest (closest to the top) 
| non-transparent pixel in the column.
| 
| 3) repeat for each column
| 
| 4) compare the results from each column to find the one that is closest to y=0
| 
Fast way...  extract the alpha channel, trim, and report the results virtual
canvas!

   convert image -alpha extract -trim -format '%wx%h%O' info:

This give you the size, and top left corner offset of the non-transparent
parts of the image.



  Anthony Thyssen ( System Programmer )    <A.Thyssen at griffith.edu.au>
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